This research is designed to determine whether exposures of human populations to levels of SO2 and particulates around the present ambient standards have an effect on the health of these populations. Random samples of adults and children have been selected in six communities with different levels of pollution and are being followed prospectively. We have completed the first six years and are about to start on our third survey of the adult population. Respiratory symptoms are obtained by means of a standard questionnaire and more objective data from tests of pulmonary function by spirometry. The exposure of the population is measured by data collected from a central station and satellite stations (about 10 per community, both indoor and outdoor). In addition, personal monitors are worn by a number of volunteers at different times of the year to determine how representative the data from the central station are for the exposure to mass respirable particulates.